EP2008287B1 - Electrical ptc thermistor component, and method for the production thereof - Google Patents

Description

Ceramic components and methods for their preparation are for. B. from the publications DE 4029681 A1 . DE 10218154 A1 . DE 4207915 A1 . DE 100 53 769 A1 and JP 01 128 501 A known.

An object to be solved is to specify a PTC thermistor component which has particularly low tolerance errors with regard to electrical properties. Another object to be solved is to provide a method for producing such a device.

The invention is defined by the features of the independent claims.

It is an electrical PTC device with a base z. B. from PTC ceramic specified. PTC stands for Positive Temperature Coefficient. The component comprises a first and a second conductive layer, which are preferably arranged on an end face of the base body. The lateral surface of the main body is free of the first conductive layer. The second conductive layer forms a cap which covers the front side of the base body across edges, this layer lying partially on the lateral surface of the base body.

In a preferred variant, in each case a first and a second conductive layer are provided on each end face. The component preferably has a mirror symmetry.

The first conductive layer is limited to the respective end face of the base body. The first conductive layer is not edge-spanning unlike the second conductive layer. The first layer contacts the main body. An end-side region of the second conductive layer is arranged on the first conductive layer, and a further region of the second conductive layer contacts the lateral surface of the main body.

The first conductive layer is preferably a barrier-degrading barrier layer. The second conductive layer, unlike the first conductive layer, is not provided as a barrier layer, but as a solder for z. B. provided with a circuit board, suitable for surface mounting electrical connection of the device.

The component is therefore preferably surface mountable. The base body is preferably rectangular in cross-section, or its lateral surface has at least one flat side surface.

Both first and second conductive layers may comprise multiple sublayers of different materials. The lower, d. H. The sub-layer of the respective conductive layer facing the base body is preferably an adhesion-promoting layer. The first conductive layer according to the invention comprises several sub-layers of different materials on z. B. a chromium-containing sub-layer as an adhesive layer on which preferably a nickel-containing sub-layer is applied.

The second conductive layer may, for. B. have a silver-containing lower sub-layer, a nickel-containing middle sub-layer and a solderable, especially tin-containing upper sub-layer. The lower silver layer can be activated with a Pd activator before nickel plating.

The lowermost sub-layer of the first conductive layer is preferably sputtered on and possibly galvanically reinforced. Further partial layers of the first conductive layer may, for. B. be applied chemically or electroplated. However, the partial layers of the first conductive layer can also be produced in each case by screen printing with subsequent baking.

The second conductive layer preferably comprises at least one applied by a dipping process layer, for. B. on a silver-containing layer. This is preferably the lowest layer of the second conductive layer. As mentioned above, at least one further layer can be applied to the lowermost layer, which can also be produced chemically or galvanically in a dipping process by screen printing.

1. A) An Hauptflächen eines großflächigen Substrats, umfassend als Bauelementbereiche vorgesehene Bereiche, wird eine Barriereschicht (erste leitfähige Schicht) durch Sputtern aufgetragen;
2. B) Das Substrat wird gemäß den Bauelementbereichen vereinzelt, wobei jeder vereinzelte Bauelementbereich einen Grundkörper umfasst, auf dessen beiden Stirnseiten die Barriereschicht angeordnet ist;
3. C) An den vereinzelten Bauelementbereichen werden stirnseitig angeordnete leitfähige Kappen (zweite leitfähige Schicht) in einem Tauchverfahren erzeugt.

Furthermore, a method for producing a PTC thermistor device is specified, with the steps:

1. A) On major surfaces of a large-area substrate comprising regions provided as device regions, a barrier layer (first conductive layer) is applied by sputtering;
2. B) The substrate is singulated in accordance with the component regions, each individual component region comprising a base body on whose two end faces the barrier layer is arranged;
3. C) Conductive caps (second conductive layer) arranged on the front side are produced on the separated component regions in a dipping process.

The large-area substrate is preferably produced by pressing a ceramic-containing material with predetermined properties and subsequent sintering. In a variant, 50% of the ceramic material ML151 and 50% of the ceramic material ML251 dry or wet homogenized, the mixture is preferably pressed on a uniaxial dry press and sintered. The substrate is lapped in a variant, preferably after sintering, preferably to a prescribed thickness, kept in a solution containing sulfuric acid for a predetermined period of time to improve the adhesion of the sputtered layer, and then washed.

To produce the barrier layer, the main surfaces of the substrate are metallized. In a preferred variant, a preferably chromium-containing layer is first applied by sputtering. The Cr layer may, for. B. be produced in a thickness of 0.1 to 1.0 microns. Thereafter, a nickel-containing layer z. B. preferably applied with a thickness of 0.1 to 1.0 microns by sputtering and galvanically or chemically reinforced to a thickness that preferably exceeds 1 micron and z. B. 2 to 10 microns. After metallization, the substrate is preferably sawn to form isolated device regions.

Before the application of caps, the edges between end faces and lateral surface of the body are rounded or at least flattened by scrubbing with the addition of water and SiC powder.

The conductive caps are applied in a dipping process, wherein each base body is immersed in a metal-containing, preferably silver-containing paste, which preferably after immersion under air atmosphere and at a temperature by Max. 900 ° C is baked. The metal layer produced in this case is preferably to produce a uniform layer thickness z. B. scrubbed and / or polished with the addition of water and SiC powder.

The conductive caps are activated after polishing preferably in the order given with Pd activator, nickel-plated and tin-plated. The nickel plating is preferably carried out chemically, d. H. de-energized. The tinning is preferably carried out galvanically. In principle, the Pd activation can be dispensed with if the nickel plating is carried out galvanically.

In the method described PTC thermistor components are generated, which are now measured, evaluated and strapped to the exclusion of ausschüssigen components.

The fact that the barrier layer is already produced before and not after the separation of the component regions in a dipping process has the advantage that the geometric dimensions determining the electrical properties of the component and thus also the manufacturing tolerances with regard to the electrical properties of the components can be kept low , Although the conductive caps are directly on the body, but they have essentially no effect on the electrical resistance of the device.

• Figur 1 ein großflächiges Substrat mit der aufgetragenen Barriereschicht und noch nicht vereinzelten Bauelementbereichen;
• Figur 2 einen vereinzelten Bauelementbereich;
• Figur 3 den vereinzelten Bauelementbereich mit abgerundeten Kanten vor dem Tauchverfahren;
• Figur 4 den vereinzelten Bauelementbereich nach dem Tauchverfahren;
• Figur 5 ein fertig gestelltes Bauelement.

The method steps for the production of the specified component will now be explained with reference to schematic and not to scale figures. Show it:

• FIG. 1 a large-area substrate with the applied barrier layer and not yet isolated component areas;
• FIG. 2 an isolated component area;
• FIG. 3 the isolated component area with rounded edges before the dipping process;
• FIG. 4 the isolated component area after the dipping process;
• FIG. 5 a finished component.

FIG. 1 shows a large-area substrate 10 with a coated on its two major surfaces barrier layer 21, 22. The substrate 10 has not yet isolated device areas 101 - 106 on. With dashed lines sawing lines, ie boundaries between different component areas are indicated.

Each component region comprises a main body 1 and barrier layers 21, 22 arranged on its end faces.

In FIG. 1 the large-area substrate 10 is formed as a rod which is sawn perpendicular to its longitudinal direction. However, the large-area substrate 10 can also have component regions arranged as a two-dimensional matrix. It is sawed in transverse directions.

In FIGS. 2 and 3 For example, a discrete device region 101 is shown before or after scrubbing. The immersed component area with silver-containing caps 31, 32, which cover its frontal ends across edges, is in FIG. 4 shown. To the front side facing edge portions of the side surfaces of the body are covered by the caps 31, 32nd

In FIG. 5 a finished component after the tinning of caps 31, 32 is shown. The barrier layer 21, 22 has a lower partial layer 211, 221 (eg Cr layer) applied by sputtering and possibly galvanically reinforced, if appropriate a chemically applied middle partial layer (eg Ni layer not shown in the figure) ) and an electrodeposited upper sub-layer 212, 222 (eg, Ni layer).

On the silver-containing cap 31, 32 produced by dipping, a tin-containing solderable layer 41, 42 is arranged. The downwardly facing portions of the caps 31, 32 form surface mounting suitable contacts of the device (SMD contacts).

The specified component and method is not limited to the embodiments shown in the figures and in particular the illustrated shape of the base body and number and material of partial layers. All layers applied by sputtering can also be produced in a dipping process or a screen printing process followed by firing.

LIST OF REFERENCE NUMBERS

1

body

10

large ceramic substrate

21, 22

barrier layer

211, 221

Sputtered partial layer of the barrier layer 21, 22

212, 222

electroplated partial layer of the barrier layer 21, 22

31, 32

conductive cap

41, 42

solderable layer

Claims (11)

1. Electrical PTC thermistor component

   - with a main body (1), which has end faces lying opposite one another and a peripheral surface,

   - with a first conductive layer and a second conductive layer, which are respectively arranged on an end face of the main body (1),

   - wherein the peripheral surface of the main body (1) is free from the first conductive layer, and

   - wherein the second conductive layer forms a cap (31, 32), which covers one end face of the main body (1) while reaching over the edges,

   - wherein the first conductive layer has a number of sub-layers of different materials.
2. Component according to Claim 1,

   - wherein the main body (1) contains a ceramic material,

   - wherein the first conductive layer is a barrier layer (21, 22) breaking down a depletion layer.
3. Component according to Claim 1 or 2,

   - wherein the second conductive layer has a solderable surface.
4. Component according to one of Claims 1 to 3,
   which is surface-mountable.
5. Component according to one of Claims 1 to 4,

   - wherein the first conductive layer has a sputtered-on sub-layer (211, 221) and a galvanically applied sub-layer (212, 222).
6. Component according to one of Claims 1 to 5,

   - wherein the second conductive layer has at least one layer applied by a dipping process.
7. Component according to one of Claims 1 to 6,
   wherein the edges between the end faces and the peripheral surface of the main body are bevelled or rounded.
8. Method for producing a PTC thermistor component, comprising the steps that:

   A) a conductive barrier layer (21, 22) is produced by sputtering on main surfaces of a substrate (10), containing PTC ceramic and comprising regions (101 - 106) intended as component regions;

   B) the substrate (10) is divided up into the component regions, wherein each divided-up component region comprises a main body (1), on the two end faces of which the barrier layer (21, 22) is arranged, wherein the peripheral surfaces of the main bodies (1) are free from the barrier layer (21, 22);

   C) conductive caps (31, 32), arranged on the end faces, are produced on the divided-up component regions, wherein they are applied by a dipping process and subsequently burned in.
9. Method according to Claim 8,
   wherein the barrier layer (21, 22) is galvanically reinforced.
10. Method according to Claim 8 or 9,
    wherein the conductive caps (31, 32) are tin-plated after the dipping process.
11. Method according to one of Claims 8 to 10,
    wherein, before the application of caps, the edges between the end faces and the peripheral surface of the main body are rounded by abrasion.

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